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| United States Patent |
5,094,934
|
|
Lazarus
, et al.
|
*
March 10, 1992
|
Method of developing a high contrast, positive photoresist using a
developer containing alkanolamine
Abstract
Compositions and methods for developing quinone diazide positive-working
photoresists. The compositions consist essentially of an aqueous solution
of a tetraalkylammonium hydroxide and an adjunct having a structure
selected from:
##STR1##
wherein n is 0 or 1; m is 1 or 2; and each R.sup.1 and R.sup.2 is
independently selected from hydrogen, methyl, or ethyl, but in Structure I
the two R.sup.2 's are not both ethyl. The methods involve use of this
composition to develop the indicated photoresists. The addition of an
adjunct of the indicated type prevents the formation of irregular deposits
on the edges of unexposed portions of the photoresist lines when the
photoresist is developed. Selection of these adjuncts also increases the
uniformity of line widths of photoresist lines developed according to the
present invention, and increases the process latitude of the developer.
| Inventors:
|
Lazarus; Richard M. (Mission Viejo, CA);
Bell; Kenneth L. (Irvine, CA);
Bauer; Carla M. (LaVerne, CA)
|
| Assignee:
|
Morton International, Inc. (Chicago, IL)
|
| [*] Notice: |
The portion of the term of this patent subsequent to February 28, 2006
has been disclaimed. |
| Appl. No.:
|
564665 |
| Filed:
|
August 7, 1990 |
| Current U.S. Class: |
430/309; 430/325; 430/331 |
| Intern'l Class: |
G03C 005/24; G03C 005/34 |
| Field of Search: |
430/309,325,331
252/79.5,156,364
|
References Cited
U.S. Patent Documents
| 3984243 | Oct., 1976 | Shimimura et al. | 430/268.
|
| 4294911 | Oct., 1981 | Guild | 430/331.
|
| 4379830 | Apr., 1983 | Deutsch et al. | 430/331.
|
| 4411981 | Oct., 1983 | Minezaki | 430/299.
|
| 4464461 | Aug., 1984 | Guild | 430/326.
|
| 4530895 | Jul., 1985 | Simon et al. | 430/145.
|
| 4729941 | Mar., 1988 | Itoh et al. | 430/331.
|
| Foreign Patent Documents |
| 0124297A | Nov., 1986 | EP.
| |
| 0231028A | May., 1987 | EP.
| |
| 56-57035 | May., 1981 | JP.
| |
| 57-42710 | Mar., 1982 | JP.
| |
| 58-82243 | May., 1983 | JP.
| |
| 60-263147 | Dec., 1985 | JP.
| |
| 61-39041 | Feb., 1986 | JP.
| |
| 396664 | Aug., 1973 | SU.
| |
| 439035 | Aug., 1974 | SU.
| |
| 2072420A | Jun., 1988 | GB.
| |
| 2193335A | Jul., 1988 | GB.
| |
Other References
Grigorovich et al., "Interaction of Photosensitive Materials, etc.",
translated from Zhurnal Prikladnoi Khimii, vol. 48, No. 6, pp. 1307-1311,
Jun., 1975.
Patent Abstracts of Japan, vol. 6, No. 209 (P-150) (1087), 21st Oct. 1982;
& JP-A-57 114 141 (Sanei Kagaku Kogyo K.K.) 15-06-1982.
European Search Report #EP 88 30 2542 of Dec. 20, 1988.
|
Primary Examiner: Bowers, Jr.; Charles L.
Assistant Examiner: Doody; Patrick A.
Attorney, Agent or Firm: White; Gerald K.
Parent Case Text
This is a continuation of co-pending U.S. application Ser. No. 07/303,506,
filed on Jan. 27, 1989 now abandoned, which in turn is a
continuation-in-part of U.S. application Ser. No. 07/160,639, filed Mar.
10, 1988, now abandoned, which in turn is a continuation-in-part of U.S.
application Ser. No. 07/035,413, filed Apr. 6, 1987, now U.S. Pat. No.
4,808,513.
Claims
We claim:
1. A method for developing an image-wise exposed quinone diazide
positive-working photoresist without forming irregular deposits on the
edges of unexposed portions of said photoresist, comprising the steps of:
A. providing said exposed photoresist;
B. providing a developer composition consisting essentially of an aqueous
solution of at least one tetraalkylammonium hydroxide, present in an
amount effective to enable said composition to develop said photoresist;
and at least one adjunct having a structure selected from the group
consisting of
##STR3##
wherein n is 0 or 1; m is 1 or 2; each R.sup.1 and R.sup.2 is
independently selected from hydrogen, methyl, or ethyl, but in Structure I
the two R.sup.2 's are not both ethyl; and the weight ratio of said
primary alkali to said adjunct is less than about 1:3;
C. developing said photoresist with said developer until the exposed
portions of said photoresist are cleared; and
D. rinsing said developer from said photoresist.
2. The method of claim 1, wherein said step C is immersion development.
3. The method of claim 1, wherein said step C is spray development and said
ratio is less than about 1:9.
4. A method for developing an image-wise exposed quinone diazide
positive-working photoresist without forming irregular deposits on the
edges of unexposed portions of said photoresist, comprising the steps of:
A. providing said exposed photoresist;
B. providing a developer composition consisting essentially of an aqueous
solution of a tetraalkylammonium hydroxide present in an amount effective
to enable said composition to develop said photoresist; and an
alkanolamine having the following structure:
##STR4##
wherein n is zero or one, each R is independently selected from hydrogen,
methyl, or ethyl, and the weight ratio of said tetraalkylammonium
hydroxide to said alkanolamine is less than about 1:3;
C. developing said photoresist with said developer until the exposed
portions of said photoresist are cleared; and
D. rinsing said developer from said photoresist.
5. The method of claim 4, wherein said step C is immersion development.
6. The method of claim 4, wherein said step C is spray development.
7. The method of claim 4, wherein said alkanolamine is
1-amino-3-hydroxypropane.
8. A method for developing an image-wise exposed quinone diazide
positive-working photoresist in a manner providing a C.sub.p value of at
least about 1.33, comprising the steps of:
A. providing said exposed photoresist;
B. providing a developer composition consisting essentially of an aqueous
solution of at least one tetraalkylammonium hydroxide, present in an
amount effective to enable said composition to develop said photoresist;
and at least one adjunct having a structure selected from the group
consisting of:
##STR5##
wherein n is 0 or 1; m if 1 or 2; each R.sup.1 and R.sup.2 is
independently selected from hydrogen, methyl, or ethyl, but in Structure I
the two R.sup.2 's are not both ethyl; and the weight ratio of said
tetraalkylammonium hydroxide to said adjunct is less than about 1:3;
C. developing said photoresist with said developer until the exposed
portions of said photoresist are cleared; and
D. rinsing said developer from said photoresist.
9. The method of claim 8, wherein said C.sub.p value is at least about 1.33
when said exposed photoresist thickness is 1.3 microns plus or minus 0.1
microns; the exposure energy used to expose said photoresist is from 150
to millijoules per square centimeter; the soft bake temperature for said
photoresist is from 110.degree. C. to 120.degree. C.; the temperature of
said developer is 19.degree. C., plus or minus 1.degree. C.; and the tool
used to expose said photoresist is focused on the upper surface of said
photoresist, plus or minus 1 micron.
10. The method of claim 8, wherein said step C is spray development and
said ratio is less than about 1:9.
11. A method for developing an image-wise exposed quinone diazide
positive-working photoresist in a manner providing a C.sub.p value of at
least about 1.33, comprising the steps of:
A. providing said exposed photoresist;
B. providing a developer composition consisting essentially of an aqueous
solution of a tetraalkylammonium hydroxide present in an amount effective
to enable said composition to develop said photoresist; and an
alkanolamine having the following structure:
##STR6##
wherein n is zero or one, each R is independently selected from hydrogen,
methyl, or ethyl, and the weight ratio of said tetraalkylammonium
hydroxide to said alkanolamine is less than about 1:3;
C. developing said photoresist with said developer until the exposed
portions of said photoresist are cleared; and
D. rinsing said developer from said photoresist.
12. The method of claim 11, wherein said C.sub.p value is at least about
1.33 when said exposed photoresist thickness is 1.3 microns plus or minus
0.1 microns; the exposure energy used to expose said photoresist is from
150 to 250 millijoules per square centimeter; the soft bake temperature
for said photoresist is from 110.degree. C. to 120.degree. C.; the
temperature of said developer is 19.degree. C., plus or minus 1.degree.
C.; and the tool used to expose said photoresist is focused on the upper
surface of said photoresist, plus or minus 1 micron.
Description
TECHNICAL FIELD
This invention relates to compositions and processes for developing quinone
diazide positive-working photoresists, particularly high contrast resists
used in the fabrication of integrated circuits on single-crystal wafers.
BACKGROUND ART
Quinone diazide positive-working photoresists and similar positive-working
compounds used in the preparation of lithographic printing plates, are
described in U.S. Pat. No. 4,464,461, issued to Guild on Aug. 7, 1984
particularly from column 3, line 39 to column 7, line 16. The foregoing
patent is hereby incorporated herein by reference. Commercial photoresists
of this kind include OFPR-800; other photoresists sold by the Dynachem
division of Morton Thiokol, Inc., Tustin, Calif.; and products sold by
Shipley Company, Inc., Newton, Mass.; Eastman Kodak Company, Rochester,
N.Y.; and others.
A positive-working photoresist functions by being coated on a suitable
substrate, image-wise exposed to actinic radiation, then subjected to a
development process which removes those portions of the photoresist which
were previously exposed to radiation, leaving the unexposed portions of
the resist intact. The developed photoresist pattern protects the
corresponding portions of the substrate from a further operation performed
on the substrate, such as ion implantation, etching, plating, or the like.
(In the case of printing plates, the residual portions of the photoresist
have a different affinity for ink than the exposed portions of the
substrate.) The known developers for quinone diazide positive-working
photoresists comprise an aqueous solution of an alkali. The concentration
of alkali is chosen to provide a developer which will selectively attack
the exposed portion of the photoresist under the exposure and development
conditions which have been selected.
While some commercially available developers contain metal salts such as
sodium carbonate, sodium hydroxide, and others as alkaline agents, the art
has recently chosen to avoid metal ion containing alkaline materials, or
other metal ion sources, in photoresist developers. A concern has
developed that residual metal ions left by the developer might form
conductive paths in the finished device. Because of this avoidance of
metal ion containing developers, the preferred alkaline materials are
tetraalkylammonium hydroxides, and particularly tetramethylammonium
hydroxide (TMAH). TMAH based developers are discussed in U.S. Pat. No.
4,423,138, issued to Guild on Dec. 27, 1983; U.S. Pat. No. 4,464,461,
issued to Guild on Aug. 7, 1984; European Patent Application 0,062,733,
filed by Cawston et al on Jan. 28, 1982 and published on Oct. 20, 1982,
based on a corresponding U.S. patent application filed Apr. 10, 1981;
Grieco et al, "Photoresist Developer Compounds", IBM Technical Disclosure
Bulletin, Volume 13, Number 7 (December, 1970); "Improved Resist
Developer," Research Disclosure 22713, March, 1983, pages 98-99; and
others.
Several prior patents show the possibility of using morpholine or an
alkanolamine, particularly ethanolamine, in photoresist developers.
According to its English language abstract, Japanese patent application
59.119105, believed to have been published Dec. 26, 1985, teaches the use
of either an inorganic alkali or an organic amine such as monoethanolamine
or ethylenediamine as an alkaline agent in a photoresist developer. U.S.
Pat. No. 4,464,461, column 1, lines 40-43, indicates that developers
containing, for example, alkanolamines are "well known". U.S. Pat. No.
4,530,895, issued to Simon et al on July 23, 1985, at column 1, lines
59-62, suggests use of a developer containing an alkaline substance such
as diethylamine, ethanolamine, or triethanolamine as a photoresist
developer. U.S. Pat. No. 4,411,981, issued to Minezaki on October 25,
1983, discloses from column 3, line 46 to column 4, line 8, the use of a
developing and etching solution for a photoresist containing various
organic bases such as TMAH, monoethanolamine, diethanolamine, or
triethanolamine, among many other basic reacting compounds. The Minezaki
patent also discloses a photoresist developer in column 5, lines 10-16,
and Table 3 comprising an aqueous solution of 5% TMAH, 1-2% morpholine,
0.04% coumarin, about 0.1% of an unspecified surfactant, and the balance
water. Minezaki states this composition is diluted double or triple with
distilled water to provide a developing and etching solution. The ratio of
TMAH to morpholine is from 1:0.4 to 1:0.2 in this composition. None of
these references suggests any reason to mix a quaternary ammonium compound
and an alkanolamine or morpholine to correct any shortcoming of either
material used alone as a developer.
As will be shown in comparative examples, TMAH used alone as a photoresist
developer causes what appears to be a deposit of flaky residue along the
upper and lower edges of lines of developer photoresists, particularly
high contrast photoresists. The presence of this residue in exposed areas
(which are intended to be free of photoresist) suggests potential
problems.
Alkanolamines by themseleves are not (suitable as developers for high
contrast photoresists of the type exemplified herein, as they develop
lines with poor resolution, fail to develop them altogether, or strip the
photoresist. High concentrations of these developers also roughen the
upper, normally smooth surface of developed photoresist lines.
One continuing challenge, as circuit geometries shrink and quality
standards are maintained or raised, is how to maximize line width
uniformity. Good line width uniformity means that lines of developed
photoresist have nearly the same nominal line width and other dimensions
as the mask lines and that these dimensions don't vary significantly
depending on the location of the line on the wafer, the location of the
wafer in a boat in which a batch of wafers are immersion processed
together, or the order in which wafers are spray processed.
Another continuing challenge in photoresist developer research is how to
achieve the desired line width uniformity despite variations from the
nominal conditions selected for development. A developer composition which
achieves this is said to have wide process latitude.
It is further desirable that a photoresist developer not cause the side
walls of the developed photoresist to become less vertical (sloped).
SUMMARY OF THE INVENTION
One object of this invention is to solve the residue problem of TMAH or
similar photoresist developers while retaining or improving the line width
uniformity and wide process latitude of such developers. A further object
is to accomplish the preceding object with a developer which is usable in
commercial automated equipment, especially ray equipment which demands
that a developer be easily sprayable.
A first aspect of the invention is a composition for developing an exposed,
quinone diazide, positive-working photoresist. The composition consists
essentially of an aqueous solution of an alkali which also contains an
adjunct. The alkali is a tetraalkylammonium hydroxide, and is present in
the composition in an amount sufficient to enable the composition to
develop the photoresist. The adjunct has a structure selected from:
##STR2##
In the above structures, n is 0 or 1; m is 1 or 2; and each R.sup.1 and
each R.sup.2 is independently selected from hydrogen, methyl, or ethyl
(except that in Structure I both R.sup.2 moieties cannot be ethyl). If m
is 2 (representing the presence of a quaternary nitrogen atom), each
R.sup.1 attached to the nitrogen atom is selected independently.
This adjunct is present in the composition in an amount sufficient to
reduce formation of the previously mentioned irregular deposits on the
edges of unexposed portions of the photoresist during development of the
photoresist. The amount of the alkali and the adjunct to be used can be
variously expressed to accomplish different objectives. For one example,
the adjunct can be present in an amount sufficient to increase the C.sub.p
value of the composition, as defined later in this specification. For
another example, the adjunct can be present in an amount sufficient to
increase the process latitude of the composition, as defined later in this
specification.
In a preferred aspect of the invention, about 0.7 to about 1.6% by weight
of the tetraalkylammonium hydroxide is present, and the ratio of the
hydroxide to the adjunct is less than or equal to about 1:3 by weight. The
composition can optionally contain from about 0 to 0.05% by weight of a
surfactant to improve the sprayability of the composition and to avoid the
problem of dewetting the resist during development.
A second aspect of the invention is a method for developing an exposed
quinone diazide positive-working photoresist without forming irregular
deposits on the edges of unexposed portions of the photoresist. The method
comprises the steps of providing an exposed photoresist for development;
providing the developer previously defined above; developing the
photoresist with the indicated developer until the pattern is cleared; and
rinsing the developer from the photoresist.
Still another aspect of the invention is a similar method in which enough
of the previously stated adjunct is present in a developer to provide a
C.sub.p value of at least about 1.33 for the developer as used to develop
a quinone diazide positive-working photoresist.
BRIEF DESCRIPTION OF DRAWINGS
FIGS. 1 through 6 are each a perspective fragmentary photographic view of a
developed two micron (nominal mask dimension) photoresist line, also
illustrating the surrounding substrate and a portion of the adjacent line.
Each photograph was taken at a magnification of 20,000 diameters, at an
energy of 23 KV, using a scanning electron microscope. FIGS. 1 through 6
show lines developed according to Examples 36 through 41, respectively.
FIG. 6 represents the state of the art prior to the present invention, and
FIG. 5 shows development using an adjunct not within the present invention
.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
Photoresist developers according to the present invention consist
essentially of a solvent, an alkali, an adjunct as defined above, and
optionally a surfactant and various other minor ingredients.
While various organic solvents are used in some photoresist developers, for
the present purpose the preferred solvent is deionized water. The amount
of water used is dictated by the amount of other ingredients. While the
amount of water is not generally critical, the compositions described
herein contain from about 60% to about 94% by weight water.
The alkali is the primary ingredient which dissolves exposed portions of
the photoresist when the photoresist is developed. Various
tetraalkylammonium hydroxides have been used or suggested as suitable
alkaline compounds; the use of any of these well known compounds is
contemplated in the broadest aspect of the present invention. (As used
herein in the context of tetraalkylammonium hydroxides, "alkyl" does not
include alkanol moieties.) The most common alkali is tetramethylammonium
hydroxide (TMAH).
The amount of alkali useful herein is most broadly more than 0.5% by
weight, preferably from about 0.7 to about 2% by weight, more preferably
from about 0.8 to about 1.6% by weight, and most preferably from about 0.9
to about 1.1% by weight. The amount of alkali used in a particular
formulation must be adjusted to account for the influence of the other
ingredients, particularly the adjuncts, which are also alkaline.
The adjuncts useful herein are those specified previously in the Summary.
Table I recites all the adjuncts within the previously stated Structure I
wherein each R.sup.2 is hydrogen. Adjuncts within Structure I in which one
or both R.sup.2 moieties are methyl or ethyl, preferably methyl (but
excluding a structure in which both R.sup.2 's are ethyl), are also
contemplated herein. Adjuncts within structure I are also called
alkanolamines herein. Adjuncts within Structure II contemplated herein
include morpholine.
As the comparative examples provided below will illustrate, several
compounds structurally related to the adjuncts specified above either
interfere with the development process or do not provide the benefits of
the present invention. Thus, diols such as propylene glycol; diamines such
as ethylenediamine; and di- or trialkanolamines have been found not to be
useful herein.
The preferred adjuncts are species 1, 2, and 10 as stated in Table I and
dimethyl-3-amine-1-propanol (DMAP). These adjuncts are all suitable for
photoresist development by immersion. Most preferred is species 10, which
has also been found to be suitable for spray development of photoresists.
The proportion of adjunct contemplated herein is determined largely by the
ratio of the alkali to the adjunct by weight. (A lower ratio indicates
less TMAH in relation to the amount of the adjunct.) For spray development
this ratio is no more than 1:9, preferably 1:12 to 1:38, and most
preferably about 1:15 if the adjunct is 1-hydroxy.3.amino-propane. For
immersion development the ratio can be as great as 1:3. The lower limits
are provided in the preferred range of ratios because when the indicated
maximum proportion of adjunct is exceeded, the surfaces of developed lines
will be roughened. The upper limits of the ranges of ratios are specified
to provide a noticeable reduction in the amount of residue formed. The
most preferred ratios have been found to minimize the residue problem at
minimal cost while avoiding the roughening effect of excess adjunct. These
ratios will be found to vary with the proportion and selection of alkali,
the choice of a particular adjunct, and the choice of immersion or spray
development.
The desired amount of adjunct will typically be from about 4% to about 40%
by weight of the composition. A preferred range is from about 14% to about
21% by weight.
The present compositions may optionally contain a surfactant, in particular
a nonionic surfactant, to improve the sprayability and wetting properties
of the formulation. In some spray development equipment, some of the
present compositions will emerge from the spray nozzle as a cohesive
stream of fluid, rather than as finely atomized droplets. The result can
be that the developer is not adequately distributed during the spray step.
The addition of certain adjuncts, particularly in large amounts, has been
found to reduce the sprayability of the compositions. This effect is
believed to result from changes in the viscosity or the surface tension of
the compositions.
Another fault which some of the present developers have is a tendency to
dewet, or withdraw from, the photoresist pattern during development. This
reduces the amount of time the photoresist pattern is exposed to the
developer, and thus inhibits development. The presence of a nonionic
surfactant alleviates this problem too.
The preferred nonionic surfactants are the polyethylene oxide condensates
of alkyl phenols. These compounds include the condensation products of
alkyl phenols having an alkyl group containing from about 6 to 12 carbon
atoms, in either a straight chain or branched chain configuration, with
ethylene oxide in amounts equal to 5 to 25 moles of ethylene oxide per
mole of alkyl phenol. The alkyl substituent in such compounds can be
derived, for example, from polymerized propylene, diisobutylene, octene,
or nonene. Examples of compounds of this type include nonylphenol
condensed with about 9.5 moles of ethylene oxide per mole of nonylphenol,
dodecyl phenol condensed with about 12 moles of ethylene oxide per mole of
phenol, dinonyl phenol condensed with about 15 moles of ethylene oxide per
mole of phenol, and diisooctylphenol condensed with about 15 moles of
ethylene oxide per mole of phenol. One particular surfactant which has
proven useful herein is TRITON X-100, marketed by Rohm and Haas Co.,
Philadelphia, Pa. The useful amount of surfactant is limited by the
tendency of such surfactants to degrade the optimal vertical wall
structure of the developed lines of photoresist, causing sloping. The
preferred composition, therefore, contains no more than about 0.05% by
weight of a nonionic surfactant. Some compositions require no surfactant
at all.
Other components, such as preservatives for TMAH, dyes, wetting agents,
cosolvents, buffers, and the like may be added to developers according to
the present invention. The preferred additives are essentially free of
metal cations.
For purposes of the present specification, the amount of alkali effective
to develop the photoresist is determined experimentally by providing a
proposed composition and varying the amount of alkali to find a
concentration which will develop the photoresist without stripping it. The
necessary amount of alkali will be determined by many factors, including
the presence of an adjunct and any other alkaline constituents of the
developer; exposure energy; line geometries; development mode and
conditions; and temperature. The examples in this specification provide
specific compositions which have been found to perform well. One of
ordinary skill in the art can readily formulate a developer having an
appropriate amount of alkali to develop a particular photoresist.
Similarly, the amount of the adjunct which is sufficient to reduce
formation of irregular deposits on the edges of unexposed portions of the
photoresist during development will depend on the developer formulation,
process conditions, the photoresist used and how it is applied, and other
factors. An amount of adjunct sufficient to reduce formation of irregular
deposits is determined qualitatively by examining scanning electron
microscope photomicrographs of photoresists developed with various
developers to select the optimal developer for a given task. When the
amount of the adjunct is expressed as an amount sufficient to increase the
C.sub.p value of the composition, C.sub.p values of the composition under
the desired development conditions are measured. The amount of adjunct is
adjusted to maximize the C.sub.p value under the desired development
conditions of at least about 1.33 when one micron lines are developed.
If the amount of adjunct is expressed as an amount sufficient to increase
the process latitude of the composition, process latitude values of the
composition are measured. The amount of adjunct is adjusted to maximize
the process latitude in a particular formulation. Preferred compositions
provide a process latitude of at least about 1.33 under the development
conditions specified in the Examples.
It is not evident from any prior art known to the inventors that selection
of the present developer compositions will allow a photoresist to be
developed under high contrast conditions without forming irregular
deposits on the edges of unexposed portions of the photoresist, providing
a C.sub.p value and a process latitude for the developer of at least about
1.33.
Various modes of development are contemplated within the scope of the
present invention. In immersion development, the coated and exposed
wafers, either alone or in a boat of wafers, are supported in a bath of
the selected developer for a sufficient time to develop the photoresists.
In spray process development individual wafers coated with the photoresist
are transported to a development site and developed by one or more
operations such as streaming the developer onto the surface of the
photoresist; spinning the wafer to remove excess material, particularly
fluid, from its surface; spraying the developer over a wide surface of the
wafer; and puddling, which is done by allowing residual developer to
remain as a meniscus or puddle covering the surface of the stationary
wafer. Automated spray development equipment can be programmed to provide
the desired selection and sequence of development steps to develop each
wafer.
EXAMPLES
The following examples are provided to illustrate practice of the present
invention, including the best mode. The claims, and not the examples,
define the scope of the present invention.
Photoresist samples were prepared as follows. The substrate was a silicon
wafer with a polyoxide surface coating, pre-treated with
hexamethyldisilane to promote adhesion. EPR-5000, a novolak resin-based
composition sold by the Dynachem division of Morton Thiokol, Inc., Tustin,
Calif., was coated onto the substrate using conventional automated
spin-coating equipment. The coating thickness was about 13,000 Angstroms
(1.3 microns), plus or minus about 300 Angstroms, and was measured for
each wafer individually. The coatings were dried and conditioned in the
usual manner, providing sensitized substrates typical of those used in the
industry.
For all experiments, the sensitized substrates were exposed through an
exposure mask on a step-and-repeat exposure tool with ultraviolet
radiation provided by a high pressure mercury vapor lamp. The size of the
exposed image (24 millimeters by 14 millimeters) allowed several exposures
(118 or less) to be distributed on the surface of the substrate without
overlapping. It was possible either to incrementally increase exposure
energies at each exposure, or to repeat one exposure energy several times
across the surface of the substrate.
Developer solutions were prepared by mixing the ingredients recited below
to provide one-gallon batches.
In the immersion testing, an entire batch of each developer solution was
poured into a large dish, forming a bath deep enough to completely immerse
a wafer being developed. The exposed substrates were developed by manually
immersing each one in the dish of developer. The immersion time was one
minute 60 seconds). Then, the substrates were removed from the dish of
developer and rinsed by placing them in a cascade tank fed from the bottom
with deionized water.
For spray/puddle development testing the development and rinsing steps were
performed using conventional automated spray development equipment sold by
Silicon Valley Group, San Jose, Calif. In each program several steps were
completed sequentially. For each step, the wafer was rotated at the
indicated rate while the indicated material was applied in the indicated
manner for the indicated amount of time, according to one of the schedules
in Table II.
Film speed of the developer was evaluated by observing through an optical
microscope at 400X magnification which of several developed one micron
lines of resist, representing different doses of radiation, were resolved.
Linewidth uniformity (Critical Dimension Uniformity) is evaluated using
several exposures at the same dose across the surface of the substrate.
Linewidth measurements are made at each of these exposures, the
measurements are averaged, and the standard deviation is calculated. A
value called "C.sub.p " can be calculated from this data according to the
following formula:
##EQU1##
Delta L is the difference between the minimum and maximum acceptable
linewidths of a line defined in the photoresist by a 1 micron line on the
exposure mask. Sigma is one standard deviation.
For a 1 micron nominal linewidth, the acceptable range of linewidths is
defined to be from 0 9 to 1.1 microns; delta L is thus (1.1-0.9) microns,
or 0.2 microns. An acceptable value of sigma is defined herein to be less
than or equal to 0.025 microns. Presenting the same information in terms
of the C.sub.p, an acceptable value for C.sub.p is defined herein to be
less than or equal to 1.33 microns.
Process latitude is a measure of a developer's ability to function
satisfactorily despite defined variations in process parameters. For
present purposes process latitude is satisfactory if, at exposure energies
of from 250 to 150 mJ/cm.sup.2 ; a resist thickness of 1.3 microns (plus
or minus 0.1 microns) of EPR-5000 resist; a (resist) soft bake temperature
of from 110.degree. C. to 120.degree. C.; a developer temperature of
19.degree. C. (plus or minus 1.degree. C.); and an exposure tool focus on
the top of the resist (plus or minus 1.0 microns); C.sub.p exceeds 1.33
microns. Process latitude can be reported quantitatively as the minimum
value of C.sub.p over the defined range of exposure energies. The
developers according to the present invention have better process latitude
than conventional resists which do not contain adjuncts.
In Examples 1-4, monoethanolamine, abbreviated "MEA", was used as an
adjunct according to the present invention. The proportions of ingredients
and other information are set out in Table III. In the Tables, development
mode "I" indicates immersion development. "Spray 1" indicates spray
development according to Program: 1 set forth in Table II. The
abbreviation "mJ/cm.sup.2 " indicates the radiation exposure in
millijoules per square centimeter. "Result" provides a qualitative
indication of the result of the experiment. LR indicates low resolution or
a lack of resolution, meaning that the developer did not selectively
remove the exposed portions of the photoresist while refraining from
attacking the unexposed portions thereof. "Poor spray" means that the
composition was not properly atomized by the spray nozzle. "Poor develop"
means that exposed portions of the photoresist were not removed or were
removed inadequately. The "ratio" is a recapitulation of the ratio of TMAH
to the adjunct, here MEA, providing a ready comparison of the development
result with the ratio of these ingredients.
Looking at Table III, it will be evident that examples 1 and 2 provide good
development in an immersion mode, while in Example 3 the spray pattern
provided during spray development was considered poor, indicating that the
material was developed but that irregular development is potentially
present. Example 4, in which only 0.5% TMAH and 80.0% MEA is employed as a
developer, demonstrates that this is too little TMAH to provide proper
development, even in the presence of 80% monoethanolamine. Example 4 also
establishes that monoethanolamine by itself, even at high concentrations,
is not a suitable developer for the present photoresist.
Table IV, in which the adjunct is 1-amino-2-hydroxypropane (species 2 of
Table I, identified in Table IV as 1,2-MPA), shows the results of Examples
5-8. In this Table and subsequent Tables, "X-100" indicates TRITON X-100
nonionic surfactant, identified previously in the specification. "Spray 2"
in the development mode line indicates Spray Develop Program 2 in Table
II. In the result column "res." indicates that a residue was present on
the edges of developed liens of the photoresist.
1-amino-2-hydroxypropane sometimes provides a residue (Examples 5 and 8 and
sometimes does not (Examples 6 and 7). It is better for immersion
development than for spray development; a poor spray pattern was noted
during spray development. The best result is obtained at a ratio of 1:18
as in Example 7, in which no residue was noted on the developed lines.
Examples 9.19 in Tables V and VI show development with
1-amino-3-hydroxypropane, abbreviated in Tables V and VI as 1,3-MPA. This
is species 10 of Table I. Looking first at Table V, Examples 9 and 10 are
essentially identical spray development runs, but in Example 9 a residue
was noted at a ratio of 1:12, while in Example 10 no residue was noted.
This indicates that this is a marginally acceptable formulation for spray
development. Similarly, Examples 11 and 12 are essentially identical spray
development runs. In one case a residue was provided, and in the other
case no residue was observed. Examples 9-12 were all run at a ratio of
1:12, which therefore is less preferred for spray development than the
1:15 ratio of Example 13. A 1:15 ratio has been found in this and other
examples of spray development to almost never leave residue on the edges
of the developed resist lines. Thus, a ratio of 1:15 is preferred to
provide optimal spray development with minimal amounts of the
alkanolamine.
Examples 14-19 show ratios of TMAH to 1,3-MPA of 1 to 3 or lower
successfully used according to the present invention. Examples 14-16,
using spray development, illustrate that the 1:15 composition of 1,3-MPA
can be sprayed successfully and provides residue free development. The
compositions of Examples 14-16 all contain TRITON X-100 surfactant, in
increasing amounts. In Example 16 0.05% of this surfactant was too much,
as it caused developed resist line sidewalls to slope or otherwise deviate
from the optimal vertical sidewalls. Thus, 0.05% of this surfactant is
more than the preferred maximum amount under the other conditions of this
example.
Examples 17, 18, and 19 illustrate the operability of ratios as high as 1:3
and as low as 1:37.9 for immersion development. Example 19 illustrates
that at extremely low ratios, even when the amount of TMAH is minimized,
the developed resist has a rough surface. Roughness is believed to be
caused by the presence of a large amount of the adjunct. While some
roughness can be tolerated, it is not desirable, so a minimum ratio of
about 1 to 38 is preferred herein.
Tables VII, VIII, and IX embody the results of comparative Examples 20-35,
using various similar compounds in place of the adjuncts of the present
invention.
In Table VII, Examples 20-24, the alkanolamine was replaced with ethylene
diamine (abbreviated EDA in the table) in ratios of from a maximum of 1:3
to a minimum of 1:37.8. In all cases immersion development was used. The
relatively large proportion of TMAH in the high ratio of Example 20
stripped both developed and undeveloped portions of the resist from the
substrate. The remaining examples all show the formation of residue or
heavy residue, and the lowest ratio of TMAH (and highest ratio of EDA)
provides a heavy residue and lack of resolution which do not constitute
suitable development. The inventors conclude from this example that a wide
range of different proportions and ratios of ethylene diamine does not
exhibit the beneficial properties of the present invention.
Table VIII provides comparative examples 25-29 in which the adjunct is
replaced with ethylene glycol (EG). Over a wide range of ratios and
proportions of ethylene glycol, the result is again a residue on the
developed lines of photoresist, in either the immersion or the spray mode
of development. Example 29 is prior art, and illustrates that a
formulation containing just TMAH in a proportion sufficient to develop the
photoresist provides a residue, and thus is not an optimal developer
according to the present invention. As noted previously, Example 4 shows
the contrary situation in which a large amount of an alkanolamine
according to the present invention is present (80%) and an insufficient
proportion of TMAH is present. Comparing these examples, it is evident
that neither TMAH alone nor an alkanolamine alone provides proper
development, but the other examples show that the combination of these two
ingredients improves development unexpectedly.
In Table IX, Examples 30 and 31 show the use of diethanolamine
(abbreviated: DEA); comparative Examples 32 and 33 show the use of
triethanolamine (abbreviated: TEA); and comparative examples 34 and 35
employ diethylethanolamine (abbreviated: DEEA) in place of the present
adjuncts. In all these comparative examples, each in two different
proportions employing the immersion development mode, development was
hindered by the additive. In Examples 30-33, despite a high maximum
exposure, only a latent image was produced. This means that the exposed
portions of the photoresist were not removed by this formulation. In
Examples 34 and 35 the developed and undeveloped portions of the
photoresist were both stripped.
The comparative examples illustrate that the class of additives which
prevent residue formation without disturbing the function of the resist
developer is narrow. Ethylene diamine differs from the adjunct
monoethanolamine by substitution of a second amine for a hydroxy group.
Ethylene glycol of comparative Examples 25-29 is different from
monoethanolamine only in that a second hydroxyl group is substituted for
the amine group. In short, a structure with an amine group on one end and
hydroxyl group on the other works, but respective structures with two
amine groups or two hydroxyl groups in the same positions do not work. The
additives of comparative examples 30-35 differ from the present adjuncts,
and specifically from monoethanolamin, because two ethyl or ethanol
moieties are substituted for the amine hydrogen atoms of the present
generic formula. Diethanolamine has two ethanol moieties instead of the
single ethanol moiety of monoethanolamine according to the present
invention. Triethanolamine has three ethanol moieties in place of the
single ethanol moiety of the present invention. Diethylethanolamine has
two ethyl groups in place of the amine hydrogens of monoethanolamine.
These substitutions provide compounds which do not function in the
advantageous manner of the resent adjuncts.
The formulations and data for Examples 36-41 are reported in Table X.
Exemplary two micron lines of each developed resist were photographed with
a scanning electron microscope at a magnification of 20,000 diameters and
an energy of 23 KV. FIGS. 1 through 6 respectively correspond to Examples
36 through 41.
In FIG. 1 and Example 36, the developer contained 1-amino-2-hydroxypropane
at a ratio of 1:12. FIG. 1 illustrates some residue, particularly along
the upper edges of the resist, but no roughness. (The slight roughness or
grain shown in the photographs on the top surface of each resist line and
on the substrate between the resist lines is a combination of noise in the
micro. scope and photographic grain.) FIG. 1 shows a reduction of the
residue problem, but not a complete solution.
In FIG. 2 and Example 37, the formulation contained the adjunct
1-amino-3-hydroxypropane at a ratio of 1:12. The result shown in FIG. 2 is
similar to that shown in FIG. 1.
In FIG. 3 and Example 38, a 1:15 ratio of 1-amino-3-hydroxypropane was
used; the formulation contained 1.00% of TMAH. As FIG. 3 shows, the
developed lines have smooth upper surfaces and no visible residue. (The
regular, horizontal striations on the sidewalls of the lines are artifacts
of standing waves in the exposure radiation, and are not residue.)
In Example 39 and FIG. 4, the ratio of TMAH to 1-amino-3-hydroxypropane is
1:37.9. The line is clearly developed and has no residue, but the entire
top and side surfaces of the line are roughened; this is considered less
than optimal development, although the advantages of the present invention
other than absence of roughness are obtained in this example.
In Example 40 and FIG. 5, ethylene diamine is added to the developer at a
ratio of 1:20. Heavy residue is present on the edges of the top surface.
The vertically oriented ridge-and-valley irregularity of the sidewalls is
also related to the presence of the residue problem.
Example 41 and FIG. 6 illustrate development with a prior art formulation
of 2.0% by weight TMAH and no other additives. FIG. 6 thus illustrates
that without an adjunct a heavy residue is observed.
In Table XI, adjuncts other than the alkanolamines of Table 1 were used
according to the present invention. In Example 42, a developer containing
morpholine was used successfully. No residue was noted, although the
developed lines had a roughened surface. DMAP
(dimethyl-3-amino-1-propanol) was successfully used in Example 43, and
neither residue nor roughened surfaces were observed.
TABLE I
______________________________________
Alkanolamine Adjunct Species
Species # Name
______________________________________
1 1-amino-2-hydroxyethane
2 1-amine-2-hydroxypropane
3 1-amino-2-hydroxybutane
4 1-hydroxy-2-aminopropane
5 2-amino-3-hydroxybutane
6 2-amino-3-hydroxypentane
7 1-hydroxy-2-aminobutane
8 2-hydroxy-3-aminopentane
9 3-amino-4-hydroxyhexane
10 1-amino-3-hydroxypropane
11 1-amino-3-hydroxybutane
12 1-amino-3-hydroxypentane
13 1-amino-2-methyl-3-hydroxypropane
14 1-amino-2-methyl-3-hydroxybutane
15 1-amino-2-methyl-3-hydroxypentane
16 1-amino-2-ethyl-3-hydroxypropane
17 2-hydroxy-3-aminomethylpentane
18 3-aminomethyl-4-hydroxyhexane
19 1-hydroxy-3-aminobutane
20 2-amino-4-hydroxypentane
21 2-amino-4-hydroxyhexane
22 2-amino-3-hydroxymethylbutane
23 2-amino-3-methyl-4-hydroxypentane
24 2-amino-3-methyl-4-hydroxyhexane
25 2-amino-3-hydroxymethylpentane
26 2-amino-3-(1-hydroxyethyl)-pentane
27 3-hydroxy-4-(1-aminoethyl)-hexane
28 1-hydroxy-3-aminopentane
29 2-hydroxy-4-aminohexane
30 3-amino-5-hydroxyheptane
31 2-hydroxymethyl-3-aminopentane
32 2-hydroxy-3-methyl-4-aminohexane
33 3-amino-4-methyl-5-hydroxyheptane
34 3-amino-4-hydroxymethylhexane
35 2-hydroxy-3-ethyl-4-aminohexane
36 3-amino-4-ethyl-5-hydroxyheptane
______________________________________
TABLE II
______________________________________
Spray Development Programs
Wafer Material Duration
Step Rotation Applied Mode of Step
______________________________________
Spray Develop Program 1
1 50 rpm Developer Spray 42 sec.
2 1,000 rpm DI water Stream
10 sec.
3 4,000 rpm None Dry 10 sec.
Spray Develop Program 2
1 1,000 rpm DI water Stream
2 sec.
2 1,000 rpm Developer Spray 10 sec.
3 400 rpm Developer Spray 5 sec.
4 0 rpm Developer Spray 2 sec.
5 0 rpm None Puddle
15 sec.
6 1,000 rpm DI water Stream
10 sec.
7 4,000 rpm None Dry 10 sec.
Spray Develop Program 3
1 450 rpm Developer Spray 7 sec.
2 50 rpm Developer Spray 4 sec.
3 0 rpm None Puddle
15 sec.
4 50 rpm Developer Spray 4 sec.
5 0 rpm None Puddle
15 sec.
6 50 rpm Developer Spray 4 sec.
7 0 rpm None Puddle
15 sec.
8 1,000 rpm DI water Stream
10 sec.
9 5,000 rpm None Dry 10 sec.
______________________________________
TABLE III
______________________________________
MEA, Examples 1-4
Component 1 2 3 4
______________________________________
Wt. % TMAH 1.60 1.00 1.00 0.50
Wt. % MEA 12.5 37.9 37.9 80.0
Wt. % H.sub.2 O
85.9 61.1 61.1 19.50
Total % 100.00 100.00 100.00
100.00
Development I I spray I
Mode
mJ/cm.sup.2 70 50 50 100
Result good good poor LR;
spray poor
develop
Ratio 1:7.8 1:37.9 1:37.9
1:160
______________________________________
TABLE IV
______________________________________
1,2-MPA, Examples 5- 8
5 6 7 8
______________________________________
Wt. % TMAH 1.25 1.25 1.00 1.05
Wt. % 1,2-MPA
15.0 15.0 18.0 21.0
Wt. % X-100 -- -- -- 0.01
Wt. % H.sub.2 O
83.75 83.75 81.00 77.94
Total % 100.00 100.00 100.00 100.00
Development I spray 2 I spray 2
Mode
mj/cm.sup.2 60 70 50 70
Result res. poor good res. and
spray poor spray
Ratio 1:12 1:12 1:18 1:20
______________________________________
TABLE V
______________________________________
1,3-MPA, Examples 9- 13
9 10 11 12 13
______________________________________
Wt. % TMAH 1.20 1.20 1.20 1.20 0.96
Wt. % 1,3-MPA
14.4 14.4 14.40 14.40 14.40
Wt. % X-100 -- -- .01 .01 .01
Wt. % H.sub.2 O
84.40 84.40 84.39 84.39 84.63
Total % 100.00 100.00 100.00
100.00
100.00
Development spray spray spray spray spray
Mode 2 2 2 2 1
mj/cm.sup.2 60 60 80 70 190
Result res. good res. good good
Ratio 1:12 1:12 1:12 1:12 1:15
______________________________________
TABLE VI
______________________________________
1,3 MPA, Examples 14- 19
14 15 16 17 18 19
______________________________________
Wt. % 1.00 1.10 1.10 1.60 0.95 0.70
TMAH
Wt. % 15.0 16.5 16.5 4.80 19.0 26.53
1,3-MPA
Wt. % X-100
.005 .01 .05 -- -- --
Wt. % H.sub.2 O
83.995 82.39 82.35 93.60 80.05 72.77
Total % 100.00 100.00 100.00
100.00
100.00
100.00
Development
spray spray spray I I I
Mode 1 1 1
mJ/cm.sup.2
110 60 70 120 50 50
Result good good side- good good rough
wall
slope
Ratio 1:15 1:15 1:15 1:3 1:20 1:37.9
______________________________________
TABLE VII
______________________________________
Comparative Examples 20- 24
Component 20 21 22 23 24
______________________________________
Wt. % TMAH 3.0 1.65 1.05 0.84 0.90
Wt. % EDA 9.0 4.95 12.6 17.4 34.02
Wt. % H.sub.2 O
88.0 93.40 86.35 81.76 65.08
Total % 100.00 100.00 100.00
100.00
100.00
Development I I I I I
Mode
mJ/cm.sup.2 10-110 50 50 50 60
Result strip res. res. res. heavy
res.;
LR
Ratio 1:3 1:3 1:12 1:20 1:37.8
______________________________________
TABLE VIII
______________________________________
Comparative Examples 25- 29
Component 25 26 27 28 29
______________________________________
Wt. % TMAH 2.40 2.55 0.87 0.90 2.2
Wt. % EG 7.20 30.6 17.40 34.02 --
Wt. % H.sub.2 O
90.40 66.95 81.73 65.08 97.8
Total % 100.00 100.00 100.00
100.00
100.00
Development I I spray spray I
Mode 2 2
mJ/cm.sup.2 60 80 70 50 50
Result res. res. res. heavy res.
res.
Ratio 1:3 1:12 1:20 1:37.8
--
______________________________________
TABLE IX
______________________________________
Comparative Examples 30- 35
Component
30 31 32 33 34 35
______________________________________
Wt. % 1.00 1.00 1.00 1.00 1.00 1.00
TMAH
Wt. % DEA
10.00 20.00 -- -- -- --
Wt. % TEA
-- -- 10.00 20.00 -- --
Wt. % -- -- -- -- 10.00 20.00
DEEA
Wt. % H.sub.2 O
89.00 79.00 89.00 79.00 89.00 79.00
Total % 100.00 100.00 100.00
100.00
100.00
100.00
Develop- I I I I I I
ment
Mode
mJ/cm.sup.2
400 400 400 400 -- --
Result latent latent latent
latent
strip strip
image image image image
only only only only
Ratio 1:10 1:20 1:10 1:20 1:10 1:20
______________________________________
TABLE X
______________________________________
Examples 36- 41
Component
36 37 38 39 40 41
______________________________________
TMAH 1.25 1.20 1.00 0.70 0.84 2.0
1,2-MPA 15 -- -- -- -- --
1,3-MPA 0 14.40 15.0 26.53 -- --
EDA 0 -- -- -- 16.8 --
X-100 0 .01 .01 -- -- --
H.sub.2 O
83.75 84.39 83.99 72.77 82.36 98.00
Total % 100.00 100.00 100.00
100.00
100.00
100.00
Develop- spray spray spray spray I spray
ment 2 1 2 3 2
Mode
mJ/cm.sup.2
70 60 110 50 50 90
Result res. slight good rough heavy heavy
poor res. res. res.
spray
Ratio 1:12 1:12 1:15 1:37.9
1:20 --
______________________________________
TABLE XI
______________________________________
Examples 42- 43
Component 42 43
______________________________________
TMAH 0.96 0.96
Morpholine 14.4 --
DMAP -- 14.4
H.sub.2 O 84.64 84.64
Total % 100.00 100.00
Development Mode I I
mJ/cm.sup.2 -- --
Result rough; good;
no res. no res.
Ratio 15:1 15:1
______________________________________
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